Cartographic devices presenting the image of a geographical map to the drivers or pilots of certain vehicles are used, particularly in aeronautics, with increasing frequency. In aerial navigation, a cartographic indicator is mainly intended to provide the aircraft pilot with a geographical map of the overflown area. The displayed area progresses in accordance with the flight and its positioning is controlled in conformity with the aircraft's longitude and latitude and optionally its heading. Latitude, longitude and heading data are supplied by the aircraft's navigation system (sensors, inertia computer, etc.). In addition to the geographical map the system concurrently displays on the cathode-ray tube a mark which indicates the location of the aircraft, together with navigation data, for example the speed, fuel consumption, and routes to be followed. Such data are frequently produced on the basis of a random-scanning mode of the cathode-ray tube in order to form symbols (vectors, circles and the like) or the alphanumeric characters to be displayed.
In order to meet the maximum needs, the geographical map on board the vehicle must be as complete as possible. However, when carrying out a particular mission, it is often disadvantageous to keep the complete map and it may be desirable that only certain details be made available. It is thus possible to avoid confusion regarding the information and the visual overburdening of the pilot while increasing the speed of intervention. Finally, the appearance of simplified images makes it possible, for example, to carry out easier navigational resettings.